Separation of air into oxygen and nitrogen by liquefaction



April 14, 1931- A. MESSER 1,800,353

SEPARATION OF AIR INTO OXYGEN AND NITROGEN BY LIQUEFACTION Filed Oct. 27, 1927 A; W MW'M Patented Apr. 14, 1931 PATIENT "OFFICE Anon nnssnn, or FRANKFOBT-ON-THE-MAIN, GERMANY SEPARATION OF AIR INTO OXYGEN AND NITROGEN BY LIQUEI'AOTION Application'file'd October 27, 1927, Serial No. 228,987, and in Germany November 15, 1926.

This invention relates to the separation of air into oxygen and nitrogen by air liquefaction and separation devices with several airseparation operations-ea g. double column 6 apparatuswhich are adapted to produce.

simultaneously pure oxygen and pure nitrogen. All the temperatures appearing in this specification will be given in degrees centigrade. The temperatures of the gases com- 1 ing ofi are, under atmospheric pressure, -195 for nitrogen and''182 for oxygen. The ases at these temperatures enter the heatymterchanger where they are used for cooling the compressed air to be used in the process. In the-column of the first pressure stage, which is at a fairly high pressure about 5 atmospheres) above atmospheric,

t ere is located the container for the crude oxygen bath which consists of about 50% of 2 oxygen and 50% nitrogen. The boiling point of this crude oxygen is about 167 at a pressure above atmospheric of 5 atmospheres.

In the container for the crude oxygen there is located a heating coil conveying compressed 2 air for evaporating the crude oxygen or maintaining the temperature necessary for its eva oration. When the air passing through the heating coilespecially in the portion of the cooling process during which it is under a pressure of about 200 atmos heres above atmospheric-is super-cooled by the very low temperature of the gases coming off 195 and 182), as happens especially in t e case of well constructed heat interchan ers, there may result such a super-cooling 0 the compressed air flowing through the heating coil as to cause evaporation in the crude oxygen bath to cease. However, if this is the casei. e., if the heating coil no longer im arts suflicient heat" to the crude oxygen bath-the separating column arranged above the latter fails on account of lackof vapour and consequently the oxygen content of this 'bathdiminishes, as isevidenced by the purity and quantity of the oxygen issuing from the column. I

The object of the invention is theremoval of the above mentioned causes that lead to the supercooling of the air and consequently of the crude oxygen bath in apparatus of the aforesaid type, and according thereto the gaseous nitrogen issuing from the top of the double column is warmed by the liquid crude oxygen obtained in the first pressure stage before it reaches the compressed air in counter-current.

In carrying out the invention, there are conducted, incounter-current to the gaseous nitrogen issuing from the upper column of the second pressure stage (low pressure portion), on the one hand liquid crude oxygen from the bath of the column of the first pressure stage and on the other hand liquid washing nitrogen from the latter in such a manner as tobring the issuing nitrogen to a fairl high temperature. Further to the same en the warmer pure oxygen obtained can be conducted to the colder nitrogen. The nitrogen warmed in this way reaches the heat interchanged for compressed air in such a warm condition that the temperature of the latter as it enters the heating coil located in the crude oxygen bath cannot be lower than the boiling point of the bath.

A further important advantage of supercooling both liquids by the cold gaseous nitrogen lies in the fact that they can be cooled before the pressure-reduction valves to a temperature that is nearly equal to that behind the pressure-reduction valves. Gonsequently, the diflerent temperatures which would otherwise obtain before and behind the pressure-reduction valves are equalized. By this means, smaller losses of vapour occur after pressure reduction.

The above mentioned heat interchange between the compressed air and the gases obtained therefrom is almost perfect. By its means thereis effected a saving in the loss of cold and consequently in the expense of the air separation.

The process has, finally, the further considerable advantage that in carrying it out a smaller total difierence of temperature has to be removed in the heat interchanger than would otherwise be the case and these temperatures can be completely equalized, so that a considerably smaller working pressure is attained. I

The process will be more fully explained I with reference to the apparatus for it out which is diagrammatically represented in the accom anying drawing. At one si e o the two-co umn apparatus A, B of known construction there is a an auxiliary heat interchanger in the tube (1' which is connected at the top with the column of the second pressure stage B by means of a pli ope E for conducting the gaseous nitrogen (hatched vertically for the sake of clearness) conducts the liquid washing nitrogen under the condenser K from the first pressure stage to the pressure-reduction valve J of the sec- .ond pressure stage. In this way there is obtained the result that in the auxiliary heat interchanger approximately the same temvperature prevails in each zone as in the corrAes%mding zone of the two-column apparatus In double column devices in which the heat of evaporation of the liquid pure oxygen is utilized for the condensation of nitrogen, there is obtained by means of the present invention an increase of'temperature and evaporation of the pure oxygen. By conducting this warmed pure oxygen into the auxiliary heat interchanger C it can likewise be used for warming the issuing nitrogen. This case is represented in the drawing, the liquid ure oxygen being taken off at the bottom 0 the condenser K and led by the coil 3 through the auxiliar heat interchanger O. In this case, the out ow tube 3a of the coil 3 is passed through the nitrogen exit pipe 4 so that the two gases enter the heat interchanger for the compressed air at absolutely the same temperature.

The usual heat interchanger for the comres sed air and for the ases obtained thererom remains unchange in its construction, but-its operationis considerably improved by connecting theretothe auxiliary heat interchanger.

Whit I claim i; h

1. pparatus or preventing t c su ercooling of the crude oxygen bath heated by compressed air in the lower portion of a twocolumn air liquefaction and separation device, comprising an auxiliary heat interchanger, means or conveying into said auxiliary heat interchanger gaseous nitrogen issuing from the top of the double-column of said liquefaction and separation device, means within said heat interchanger for conducting, in counter-current to said gaseous nitrogen, liquid crude oxygen obtained in the first pressure stage of said liquefaction and separation device, and means for conducting 2. Apparatus for preventing the su cooling of the crude oxygen bathhea'tetfliy compressed air in; the lower rtion of a twocolumn air li uefaction an separation device, comprising an auxiliary 'heat exchanger, means for conveying into said auxiliary heat interchanger gaseous nitrogen issuing from the top of the double-column of said liquefaction and separation device, means within said heat interchanger for conducting, incounter-current to said'gaseous nitrogen, liquid crude oxygen obtained in the first pressure stage of said liquefaction and separation device, means within said heat interchanger for conducting, in counter-current to said gaseous nitrogen, liquid nitrogen ob- .tained in the first pressure stage, and means for conducting the warmed gaseous nitrogen for counter-current to cool the compressed 8.11. i

3. Apparatus for preventing the supercooling of the crude oxygen bath heated by compressed air in the lower portion-of a twocolumn air .liquefaction and separation device, comprising an auxiliary heat inter-' changer, means for conveying into 'said auxiliary heat interchanger gaseous nitrogen issuing from the top of the double-column of said liquefaction and separation device,

means within said heat interchanger for conducting, in counter-current to said gaseous nitrogen, liquid crude oxygen obtained in the first pressure stage of said liquefaction and separation device, and means for conducting the finished oxygen and warmed gaseous nitrogen in thermal contact with each other to the compressed air.

4. Apparatus for preventing the supercooling of the crude oxygen bath heated by compressed air in the lower portion of a twocolumn air liquefaction and separation device, comprising an auxiliary heat interchanger, means for conveying-into said auxiliary heat interchanger gaseous nitrogen issuing from the top of the double-column of said liquefaction and separation device, means within said-heat interchanger for conducting, in counter-current to said gaseous nitrogen, liquid crude 0 gen obtained in the first pressure stage 0 said liquefaction and separation device, means within said heat interchanger for conducting, in countercurrent to said gaseous nitrogen, liquid nitrogen obtained in the first pressure stage, and means for conducting the finished oxygen and warmed gaseous nitro en inthermal contact with each other 0 the compressed air.

5. The combination with a two column air liquefying' and separating apparatus, of a heat interchanger of the countercurrent type having means for conveying through said heat interchanger in one direction the gaseou -the warmed I countercurrent to cool the nitrogen from the top of the lower pressure column of said apparatus, and means for conveying through said heat interchanger in the o posite direction crude liquid oxygen from t e bottom of the higher pressure column to the lower pressure column intermediate of the ends of thelatter. I

6. The combination with a two column air liquefying and separating apparatus, of a heat interchanger of the countercurrent type having means for conveying through said heat interchanger in one direction the gaseous nitrogen from the top of the lower pressure column of said apparatus, and means for conveying through said heat interchanger in the opposite direction condensate from the upper end of the higher pressure column to theupper end of the lower pressure column.

7. The combination with a two column air liquefying and separating apparatus, of

- a heat interchanger of the countercurrent t 0 having means for conveying through said heat interchanger in one direction t e gaseous nitrogen from the top of the lower pressure column of said apparatus, means for conveying through said heat interchanger in the opposite direction crude-liquid oxygen from the bottom of the higher pressure column to the lower pressure column intermediate of the ends of the latter, and means for conveying through said heat interehanger inthe last mentioned direction condensate from the upper end of the hi her pressure column to the upper end of the owerfu'essure column.

- n testimony whereof I have signed my name this 27th day of Se tember 1927.

p AD LF MlJSSER. 

